On a railcar, wheeled trucks support opposite ends of a railcar body for movement over tracks. Each truck includes a bolster extending essentially transversely of the car body longitudinal centerline. In the preponderance of freight cars, a pivotal connection is established between the bolster and railcar body by center bearing plates and bowls transversely centered on the car body underframe and the truck bolster. Accordingly, the truck is permitted to pivot on the center bearing plates under the car body. As the railcar moves between locations, the car body also tends to adversely roll from side to side.
Attempts have been made to control the adverse roll of the railcar body through use of side bearings positioned on the truck bolster outwardly of the center bearing plates. A “gap style” side bearing has been known to be used on slower moving tank/hopper railcars. Conventional “gap style” side bearings include a metal, i.e. steel, block or pad accommodated within an elongated open top pocket or recess defined on the truck bolster. An elongated and upstanding housing or cage, integrally formed with or secured, as by welding or the like, to an upper surface on the truck bolster defines the open top recess and inhibits sliding movement of the metal block relative to the bolster. The recesses provided on the bolster can, and often do, differ in size relative to each other. As is known, a gap or vertical space is usually present between the upper surface of the “gap style” side bearing and the underside of the railcar body.
Other conventional “gap style” side bearings have included roller bearings carried for rolling movements within the elongated housing or carrier mounted on the upper surface of the railcar bolster. The roller extends above an uppermost extent of the housing or carrier and engages with an underside of the railcar body. Such side bearings are able to support the railcar body with respect to the bolster while at the same time permitting the bolster, and therefore the truck, freedom to rotate with respect to the car body as is necessary to accommodate normal truck movements along both straight and curved track.
Under certain dynamic conditions, combined with lateral track irregularities, the railcar truck also tends to oscillate or “hunt” in a yaw-like manner beneath the car body. The coned wheels of each truck travel a sinuous path along a tangent or straight track as they seek a centered position under the steering influence of the wheel conicity. As a result of such cyclic yawing, “hunting” can occur as the yawing becomes unstable due to lateral resonance developed between the car body and the truck. As will be appreciated, excessive “hunting” can result in premature wear of the wheeled truck components including the wheels, bolsters, and related equipment. Hunting can also furthermore cause damage to the lading being transported in the car body.
Track speeds of rail stock, including tank/hopper cars, continue to increase. Increased rail speeds translate into corresponding increases in the amount of hunting movements of the wheeled trucks. As will be appreciated, “gap style” or those side bearings including roller bearings cannot and do not limit hunting movements of the wheeled trucks. As such, the truck components including the wheels, bolsters, and related equipment tend to experience premature wear.
The art has also contemplated constant contact side bearings for railcars. Constant contact railcar side bearings not only support a railcar body with respect to the bolster during relative rotational movements therebetween but additionally serve to dissipate energy through frictional engagement between the underside of the railcar body and a bearing element thereby limiting destructive truck hunting movements. Most constant contact side bearings typically include a housing assembly including a base and a cap. The base usually has a cup-like configuration and includes at least two apertured flanges, extending in opposed radial directions relative to each other, permitting the base to be suitably fastened to the bolster. In one form, the cap is biased from the base and includes an upper surface for contacting and rubbing against a car body underside. As will be appreciated, the cap is free to vertically move relative to the side bearing base. Such constant contact side bearings furthermore include a spring.
The purpose of such spring is to absorb, dissipate, and return energy imparted thereto during a work cycle of the side bearing assembly and resiliently position the upper surface of the cap, under a preload force, into frictional contact with the car body underframe. The spring for such side bearings can comprise either spring loaded steel elements or elastomeric blocks or a combination of both operably positioned between the side bearing base and the cap. An elastomeric block which has been found particularly beneficial is marketed and sold by the Assignee of the present disclosure under the tradename “TecsPak.” As will be appreciated, however, such an elastomeric block, by itself, lacks longitudinal stiffness and, thus, requires surrounding housing structure to provide added support and stiffness thereto.
Known constant contact side bearings are simply not designed to fit or be accommodated within existing pockets or recesses on a truck bolster of a railcar. The attachment flanges or lugs radially extending from opposed sides of the housing structure or base consume valuable space and inhibit such a known bearing assembly from fitting into the open top recess defined by the cage or carrier present on the railcar truck bolster. Accordingly, to use a constant contact side bearing on railcar having a bolster with a recess defined by such cage or carrier requires either replacement of the entire truck bolster or complete removal of the upstanding housing or cage, defining the pocket, from the surface of the bolster to which the attachment flanges or lugs of the side bearing are normally secured. Either proposal requires extensive manual efforts and, thus, is expensive while keeping the railcar out of revenue service for an extended time period.
Although usable with a solid steel block or roller bearings, the restrictive space constraints inherent with the open top cage or carrier on a railcar bolster are a significant concern when considering fitting a constant contact railcar side bearing assembly into such structure. As known, an elastomeric spring deforms outwardly when a compressive load is placed thereon and requires substantial space around it for lateral or radial expansion or deformation. As will be appreciated, without adequate space surrounding the elastomeric spring, the radial deformation of the elastomeric spring, resulting from axial compression thereof, may cause the periphery of the elastomeric spring to press against the surrounding side bearing housing structure which could result in “stiction”, and a substantial increase in the spring rate, and, in some instances, irreparable damage to the surrounding side bearing housing structure.
When considering use of a railroad car side bearing in a recess defined by a cage on a railcar bolster only limited space is available. That is, the size of the recess defined by the cage on the railcar bolster restricts the size of the side bearing assembly and, thus, the size of the elastomeric spring which can arranged in combination therewith. Of course, restricting spring size likewise restricts the force capable of being developed by such spring. If the spring arranged in combination with the railcar side bearing assembly is too small, the force capable of being developed by such spring may be insufficient to permit the side bearing assembly from exerting the required force against the underside of the car body to prevent rolling movements and inhibit “hunting” movements of the associated wheeled railcar truck. Also, the space consumed by the side bearing housing, arranged in surrounding relation relative to the elastomeric spring, still furthermore reduces the size of the envelope for accommodating such a spring thus adversely affecting the preload force required to be developed by the railroad car side bearing.
Some railcar designs further exacerbate the problem of fitting a constant contact side bearing thereto. In many railcar designs, the side bearing operates within a five and one-sixteenth inch nominal working space between the truck bolster and the car body underside. Such dimension usually provides sufficient space for the spring to develop the required preload force for the side bearing. In other railcar designs (i.e., tank/hopper railcars), however, the vertical space between the bolster, to which the side bearing is secured, and the car body underside is severely restricted. In fact, some railcar designs provide only about a two and five-eights inch nominal working space between the truck bolster and the underside of the railcar. The reduced work space envelope provided on many railcar designs is too limited to accommodate a constant contact side bearing designed to develop sufficient force to control such hunting movements.
Additionally, heat buildup in proximity to an elastomeric spring of constant contact side bearings is a serious concern. While advantageously producing an opposite torque acting to inhibit the yaw motion of the truck, the resulting friction between the side bearing and underside of the car body develops an excessive amount of heat. The repetitive cyclic compression of the elastomeric block coupled with high ambient temperatures, in which some railcars operate, further exacerbate spring deformation. As will be appreciated, such heat buildup often causes the elastomeric block to soften/deform, thus, significantly reducing the ability of the side bearing to apply a proper preload force whereby decreasing vertical suspension characteristics of the side bearing resulting in increased hunting.
Thus, there is a continuing need and desire for a constant contact railcar side bearing assembly including an elastomeric spring capable of developing the force necessary to accomplish those goals mentioned above and wherein the elastomeric spring and railcar side bearing are configured to fit within only those limited space constraints provided by the open top cage or carrier on the railcar truck bolster.